Let people deregister, I see no reason to force someone on the voter rolls against their will. A ban would be utterly pointless because deregistering does no harm to the game, the drama queens who rage quit because they lost an election are going to be drama queens, a dereg ban wouldn't solve that, it would just simply move their whining from the New Register Thread to its own dedicated thread.
And regarding the "What's wrong with just deleting campaign PMs?" point, I don't get why we should still go out of our way to inconvenience people with messages about a game they want nothing to do with. It's all just a hassle that could simply be solved by one post in the registration thread followed by two clicks on Peebs' mouse.
Let them deregister and not come back for 6 months!
I'm perfectly content with an extension of the current rereg cooldown. In fact, I actively support it as it allows the people who actually want to deregister forever or for an extended period of time to do that while keeping the drama queens from doing their Shakespearean exits before popping up two weeks later.